Ambrx Announces First Patient Dosed in a Phase 1 Trial for ARX517, an ADC in Development to Treat PSMA Expressing Tumors

Ambrx (NYSE: AMAM), a clinical stage biopharmaceutical company using an expanded genetic code technology platform to create Engineered Precision Biologics, today announced the first patient has been dosed in a Phase 1, multicenter, open-label, dose-escalation, and dose expansion study to evaluate the safety, pharmacokinetics (PK), and anti-tumor activity of ARX517 in subjects with prostate specific membrane antigen (PSMA) expressing tumors found in prostate, pancreatic, lung and ovarian cancers.

ARX517 is an anti-PSMA antibody drug conjugate (ADC) that demonstrated activity in both enzalutamide sensitive and resistant preclinical models for prostate cancer while demonstrating favorable PK and toxicity profiles in IND-enabling GLP toxicity studies.

“I am excited to announce that we dosed our first patient in our Phase 1 trial, and thus have taken the first steps in evaluating the potential clinical benefit of ARX517 in cancer patients with tumors overexpressing PSMA,” said Feng Tian, Ph.D., Chairman of the Board, President and CEO of Ambrx. “ARX517 is the second ADC in our internal pipeline to enter the clinic, which I believe speaks to the broad applicability and productivity of our technology platform. I look forward to updating you on the progression of this trial.”

The Phase 1 trial will be a multi-center, open-label, dose escalation and dose expansion study. This trial, referred to as APEX-01, is designed to assess the safety, tolerability and PK profile, as well as the anti-tumor activity, of ARX517 as a monotherapy. The trial will enroll up to 76 patients with advanced solid tumors whose diseases have failed prior standard therapies.

About PSMA, prostate cancer and other solid tumors

PSMA has been found highly expressed in prostate cancer, particularly in metastatic castration-resistant prostate cancer (mCRPC). Additionally, PSMA has been found in a variety of other solid tumors. Prostate cancer represents a significant unmet need and sizable market opportunity. There were 1.3 million new cases of prostate cancer with five-year survival rates of approximately 27% and 359,000 associated deaths worldwide in 2018. For men, prostate cancer is the second most frequent cancer and the fifth leading cause of cancer death. The global market for prostate cancer therapies was estimated to be $9.3 billion in 2018 and is forecast to grow to $12.8 billion by 2028. While non-ADC therapies are available to treat mCRPC, there is no approved therapy specifically targeting PSMA to treat prostate cancer.

About Ambrx

Ambrx is a clinical stage biopharmaceutical company using an expanded genetic code technology platform to discover and develop Engineered Precision Biologics. These include next generation antibody drug conjugates (ADCs), bispecifics, targeted immuno-oncology therapies, novel cytokines to modulate the immune system, and long-acting therapeutic peptides for metabolic and cardiovascular disease. Ambrx is advancing a robust portfolio of clinical and preclinical programs designed to optimize efficacy, safety and ease of use, in multiple therapeutic areas, including its lead product candidate ARX788. In addition, the company has clinical collaborations with Bristol Myers Squibb, BeiGene, Sino Biopharma, Elanco and NovoCodex, for drug candidates generated using Ambrx technology. For additional information, please visit www.ambrx.com.

Forward Looking Statements

This press release contains forward-looking statements, including, but not limited to, statements related to the potential benefits of ARX517; the expected scope, endpoints and timing of the APEX-01 clinical trial; projected growth in the market for prostate cancer; and other statements that are not historical facts. These forward-looking statements are based on Ambrx’s current expectations and inherently involve significant risks and uncertainties. Actual results and the timing of events could differ materially from those anticipated in such forward-looking statements as a result of these risks and uncertainties, which include, without limitation, risks related to clinical trials, including the fact that prior results may not predict future clinical trial outcomes; impacts of the COVID-19 pandemic and actions taken to slow its spread, including potential delays in clinical trials; regulatory obligations and oversight, including any changes in the legal and regulatory environment in which Ambrx operates and those risks detailed from time-to-time under the caption "Risk Factors" and elsewhere in Ambrx’s filings and reports with the Securities and Exchange Commission. Ambrx undertakes no duty or obligation to update any forward-looking statements contained in this press release as a result of new information.

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